The authors of this volume, being familiar with the development of the art of underpinning from its rather crude methods in 1900 to its present highly developed state, and having unusual opportunities to gather valuable first-hand material through the generosity of Smith, Hauser & MacIsaac, Inc., whose contract involved the greatest amount of underpinning incidental to any one contract on subway work, have been impelled to make this fund of information available to engineers and contractors. During the progress of construction on William Street throughout two years, great pains were taken to photograph the essential steps in underpinning, supplementing these with drawings and scientifically altered photographs. It was felt that one good illustration was worth many pages of description, and every effort was made to gather a complete set. Just enough text was added, it is hoped, to sufficiently supplement the illustrations. As the engineer has usually only a very limited time at his disposal, the book is so arranged that almost without the text he may quickly get correct and accurate ideas as to the proper methods of underpinning.
